1. Technical Field
The present invention relates to test terminals for use in electrical primary power distribution circuits. In particular, the invention relates to test terminals which are placed directly in electrical series with power lines which connect to high-voltage transformers or reactors at their bushing stud members. The test terminal is placed directly in mechanical as well as electrical series with power lines leading to and from transformers and reactors at their inlet and outlet bushing stud members. The terminals carry the full current in the lines when they are closed and facilitate electrical isolation of the transformer or reactor when open to test induced electrical currents such as by Doble testing. The terminals maintain structural integrity in the lines at a level sufficiently strong to physically support the lines under adverse weather conditions which may mechanically overload the lines and terminals when connected to the bushing stud members. The present invention further relates to maintaining the insulator portion of the terminal in compression rather than tension and substantially shortens the moment arm of the terminal to withstand severe mechanical as well as high-voltage electrical loading.
2. Background Information
The most common types of test terminals for electrical power distribution systems, for interconnection to transformers and reactors having bushing studs projecting upwardly therefrom, have employed vertical post-type insulators which are terminated by end fittings and have vertical bus bars or connectors extending vertically between the fittings. A common type of such terminal is the so-called Lapp terminal having a vertical post-type ceramic insulator connected to upper and lower metal fittings such as by high temperature cement. It is most common for the end fittings to be cylindrical in shape with the insulator also being cylindrical. A pair of heavy electrical cables is connected directly to the upper fitting in vertical alignment with or at a right angle to the stud and the lower fitting is connected to the upwardly-projecting bushing stud. In such arrangement the vertical insulator is frequently placed in tension with the bushing stud carrying the entire mechanical load of the terminal and interconnected power lines. When the lines become mechanically overloaded such as by coatings of ice and high winds, the terminal insulator component is severely stressed which can cause terminal or stud breakage resulting in power outages which are difficult and time-consuming to repair. It is not uncommon for the transformer bushing stud to be bent out of vertical alignment with the transformer body which can adversely affect transformer performance or cause its failure.
It is well known in the art that continuance of positive angular orientation between the mounting surfaces of the insulator end fittings and the mating surfaces of the mounting hardware to be joined must be established and that positive mechanical and electrical connection must be maintained. When the interconnected power lines are unduly stressed, the lengthy vertical moment arm of the Lapp terminal which is normally mounted at a substantially right angle to the incoming power lines places severe torsional stress as well as tensile stress on the insulator and its interconnecting surfaces. In some cases the lengthy post-type insulator of the Lapp terminal may slip out of the U-bolt type fasteners employed to retain the insulator ends causing electrical malfunction. Also, in some cases, the insulator requires a metallic supporting ring around a medial body portion for increased mechanical strengthening of the ceramic insulator. In addition, the Lapp terminal employs a pair of parallel upright bus bars connected to the upper and lower fittings of the terminal bars which are rigidly bolted to such fittings and are not capable of ready disconnect for testing of induced electrical current. One of the most severe problems with the Lapp terminal is the high vertical moment arm which places the insulator in tension when supporting the interconnecting ends of the power lines, normally two of which are mounted in parallel. Where the post-type insulator of the Lapp terminal is supported at its ends by U-shaped bolts or retention members, the insulator member may be subject to breakage such as wherever the power lines and supporting terminal are severely stressed when covered with heavy coatings of ice or are whipped by high winds, for example.
While the common types of test terminals utilized in the industry have had suitable electrical capability for their intended interconnection purposes, many such terminals have not provided sufficient mechanical capability even though they have been constructed from heavy components which are physically similar to the Lapp terminal. Problems encountered of applying additional cantilevered force on the high-voltage equipment, and especially torsional forces exerted on the ceramic insulator component, have been a source of malfunction in high-voltage lines such as those delivering 345 kilovolts and above. Increased maintenance of such lines due to their terminal connection has necessitated the advent of this invention.